BOOK III.

DEVIATIONS FROM THE ORDINARY NUMBER OF ORGANS.

To a certain extent the number of the organs of a plant is of even greater consequence for purposes of cla.s.sification than either their form or their arrangement; for instance, the number of cotyledons in the embryo is made the chief basis of separation between the two great groups of flowering plants, the monocotyledons and the dicotyledons. In the one group, moreover, the parts of the flower are arranged in groups or whorls of five; in the other the arrangement is ternary. In mosses the teeth of the peristome are arranged in fours, or in some multiple of that number. So far as the larger groups are concerned, and also in cases where the actual number of parts is small, the numerical relations above described are very constant; on the other hand, in the minor subdivisions, and especially where the absolute number of parts is large, considerable variation may occur, so that descriptive botanists frequently make use of the term indefinite, and apply it to cases where the number of parts is large and variable, or, at any rate, not easy to be estimated.

Considered teratologically, the changes, as regards the number of organs, are readily grouped into those consequent on a decreased and into those resulting from an increased development. The alteration may be absolute or relative. There may be an actual deficiency in the number of parts or an increase in their number, but in either case the change may be simply a restoration of the primitive number, a species of peloria, in fact. An increased number of parts, moreover, may depend not so much on the formation of additional parts as on the subdivision of one.

It seems also desirable to treat separately those cases in which there is an increased number of buds either leaf-buds or flower-buds, as the case may be, as happens in what is termed prolification. This formation of buds occurring, as it does, often in unwonted situations is treated of under the head of alterations of arrangement, the mere increase in number being considered of subordinate importance as contrasted with the altered disposition (see p. 100).

PART I.

INCREASED NUMBER OF ORGANS.

An augmentation in the number of parts may arise from several causes, and may sometimes be more apparent than real. True multiplication exists simply as a result of over-development; the affected organs are repeated sometimes over and over again each in their proper relative position, and without any trans.m.u.tation of form.

Metamorphy, on the other hand, often gives rise to the impression that parts are increased in number, when it may be that the stamens and pistils, one or both, are not so much increased in number as altered in appearance. The double anemones and ranunculus of gardens, amongst many other a.n.a.logous ill.u.s.trations, may be mentioned. In these flowers, owing to the petalody of the stamens and pistils, one or both, an impression of exaggerated number is produced, which is by no means necessarily a true one. Fission or lateral subdivision also gives rise to an apparent increase in number; thus, some so-called double flowers, the elements of which appeared to be increased in numbers, owe the appearance merely to the laciniation or subdivision of their petals.

The French botanists, following Dunal and Moquin, attribute an increase in the number of whorls in the corolla, and other parts of the flower, to a process which they call chorisis, and they consider the augmentation to be due to the splitting of one petal, for instance, into several;--somewhat in the same manner as one may separate successive layers of talc one from the other.

English botanists, on the other hand, have been slow to admit any such process, because, in most instances, no alteration in the law of alternation takes place in these double flowers, and in those few cases where the law is apparently infringed, the deviation is explained by the probable suppression of parts, which were they present would restore the natural arrangement of the flower; and, that this is no imaginary or purely theoretical explanation, is shown by some of the _Primulaceae_, wherein a second row of stamens is occasionally present in the adult condition, and renders the floral symmetry perfect.

The double daffodil, where there are from forty to fifty petaloid organs instead of fifteen, and wherein each piece exhibits a more or less perfect coronal lobe at the junction of the claw and the limb, has been cited as an objection to chorisis, though it is difficult to see on what grounds.

In _Delphinium_, as shown by Braun,[376] the stamens and carpels are members of a continuous spiral series, and in the double balsam an extra corolline whorl is produced, without the suppression of the stamens, in the following manner: the ordinary stamens are replaced by petals, the carpels by stamens, while an additional whorl of carpels is produced at the summit of the axis. In this instance, therefore, the doubling is distinctly referrible to an absolute increase in the number of whorls, and not to chorisis.[377]

On the other hand, it must be admitted that there are many cases which are not to be explained in any other way than that suggested by the French botanists before alluded to. Probably, the main difficulty in the way of accepting the doctrine of chorisis is the unfortunate selection of the word used to designate the process; this naturally suggests a splitting of an organ already perfectly formed into two or more portions, either in the same plane as the original organs, "parallel chorisis;" or at right angles to it "collateral chorisis." Indeed, before so much attention had been paid to the way in which the floral organs are developed, it was thought that an actual splitting and dilamination did really take place; Dunal and Moquin both a.s.sert as much. The truth would rather seem to be that, in the so-called parallel chorisis at least, the process is one of hypertrophy and over-development rather than of splitting. The advent.i.tious petal or scale is an excrescence or an outgrowth from the primary organ, and formed subsequently to it.

In the case of "compound stamens" the original stamens are first developed each from its own cellular "mamelon," or growing point; and, after a time, other secondary growing points emerge from the primary one, and in this way the stamens are increased in number, without reference, necessarily, to the so-called law of alternation. Outgrowths from leaves, multiplying the laminar surface, are alluded to under the head of hypertrophy, and it is probable that some of the cases of duplication of the flower, or of the formation of advent.i.tious segments outside the ordinary corolla as alluded to in succeeding paragraphs (see Pleiotaxy of the corolla), are due to a similar process.[378]

The formation of parts in unwonted numbers may be merely a reversion to what is supposed to have been the original form, and in this way there may be a restoration of parts that are usually undeveloped or suppressed. There can be little or no doubt that there are in reality six stamens in _Orchidaceae_, of which one only, under ordinary circ.u.mstances, is developed. When the numerical symmetry is restored, as it sometimes is, it is obvious that the augmentation that occurs is of a different character from that arising from a repet.i.tion or renewed development of organs. When the increased number arises from multiplication proper, or from repet.i.tion, the ordinary laws of alternation are not interfered with, but if from chorisis or "dedoublement," it may happen that the normal arrangement is disturbed.

Without studying the mode of development, it is not in all cases possible to tell under which of the above categories any particular instance should be placed; hence, in the following sections, except where otherwise stated, the cases are grouped according to the appearance presented in the adult condition, rather than to the way in which the changes from the typical condition are brought about. With reference to the foliar organs it is necessary to distinguish those cases in which there is, from any cause, an augmentation in the number of component parts of a whorl, from those in which the increase takes place in the numbers of the whorls themselves.

FOOTNOTES:

[376] Braun, 'Pringsheim Jahrbuch f. Wiss. Bot.,' 1858, 1, p. 307, tab.

22, 23.

[377] Henfrey, 'Jour. Linn. Soc. Bot.,' vol. iii, p. 159.

[378] On the subject of chorisis or dedoublement the reader may profitably consult Moquin-Tandon, 'Ess. sur les Dedoublements,' and the same author in 'Ann. Sc. Nat.,' t. xxvii, p. 236. and 'El. Ter. Veget.,'

p. 337. Dunal, 'Consid. Org. Fleur.,' Montpell., 1829, p. 32, note 3. A.

de St. Hilaire in 'Ann. Sc. Nat.,' ser. 3, t. iii, p. 355, adnot.

Lindley, 'Elements of Botany,' p. 76. Asa Gray. 'Botanical Text Book.'

CHAPTER I.

MULTIPLICATION OF AXILE ORGANS, INFLORESCENCE, ETC.

By Linne an undue number of branches was designated as "plica," from the a.n.a.logy with the disease of the hair known as plica polonica: "_Plicata dicitur planta, c.u.m arbor vel ramus excrescit minimis intertextis ramulis, tanquam plica polonica ex pilis, ceu instar nidi Picae, quod vulgo a genio ortum arbitratur; frequens apud nos in Betula, praesertim Norlandiae, in Carpino Scaniae, nec infrequens in Pinu._"[379]

By some of the older authors this condition was called polyclady. In some cases, it would seem to be due to fungi as in the witches' brooms (hexenbesen) of the German forests; in other instances, it is a result of mutilation as after the operation of pollarding.

Moquin-Tandon[380] mentions a case in a grafted ash in the botanic garden of Toulouse, where below the graft there was a large swelling, from which proceeded more than a thousand densely-packed, interlacing branches.

This must have been similar to the condition so commonly met with in the birch, and frequently in the hornbeam and the thorn, and which has prompted so many a schoolboy to climb the tree in quest of the apparent nest. It is probable that some of the large "gnaurs" or "burrs," met with in elms, &c., also in certain varieties of apples, are cl.u.s.ters of advent.i.tious buds, some of which might, and sometimes do, lengthen out into branches.

An increased number of branches also necessarily arises when the flower-buds are replaced by leaf-buds.

[Ill.u.s.tration: FIG. 179.--Flower stalks of _Bellevalia comosa_, nat.

size, after Morren.]

Occasionally, a great increase in the number of pedicels, or flower-stalks, may be met with in conjunction with a decreased number of flowers, as in the wig-plant (_Rhus Cotinus_), or the feather-hyacinth (_Bellevalia comosa_). In these cases the supernumerary pedicels are often brightly coloured. To this condition Morren gave the name mischomany, from [Greek: mischos], a pedicel, a term which has not generally been adopted.[381]

[Ill.u.s.tration: FIG. 180.--Tuft of branches at the end of the inflorescence of _Bellevalia comosa_, enlarged after Morren.]

M. Fournier[382] describes a case in the butcher's broom (_Ruscus aculeatus_), wherein from the axil of the minute leaf subtending the flower a secondary flattened branch proceeded.

Duchartre[383] cites the case of a hyacinth which, in addition to the usual scape, had a second smaller one by its side terminated by a solitary flower; indeed, such an occurrence is not uncommon.

Some tulips occasionally present three or four, or more, flowers on one inflorescence, but whether from a branching of the primary scape, or from the premature development of some of the axillary bulbils into flowering stems which become adherent to the primary flower-stalk, cannot, in all cases, be determined. Certainly, in some cases examined by me the latter was the case.[384]

Under this head, too, may be included those cases wherein an ordinarily spicate inflorescence becomes paniculate owing to the branching of the axis and the formation of an unwonted number of secondary buds.

Instances of this kind may be met with in willows, hazels, alders, and other amentaceous plants. In the case of the hazel the unusual development of male catkins sometimes coincides with an alteration in their position, instead of being placed near the axil of a leaf; they become terminal. Jaeger figures and describes a bunch of _Pinus sylvestris_ bearing in one case seventy minute cones, and in another fifty-nine. These cones preserved the same spiral arrangement among themselves which is proper to the leaves. These latter, indeed, replaced the strobili above.[385]

[Ill.u.s.tration: FIG. 181.--Increased number of male catkins in the hazel _Corylus avellana_.]

M. Reichardt describes an a.n.a.logous case in the same species, and attributes the inordinate number of cones to a fungus (_Peridermium pini_). In this case there were no less than 227 cones, but each one half the size of the ordinary cones.[386]

Of a similar character is the many-headed pineapple. Among gra.s.ses such a branching of the inflorescence is exceedingly common,--which is the more readily understood as the normal inflorescence is in so many cases paniculate. Cultivators have, in some instances, availed themselves of this peculiarity, as in the Egyptian wheat or corn of abundance (_Tritic.u.m compositum_), certain varieties of Maize, etc. Similar exuberant growths occur in _Orchidaceae_, in _Cyperaceae_, e.g. _Carex_, in _Restiaceae_, and indeed they may be found in any plant with a similar form of inflorescence. In all these cases the branching begins at the lower part of the spike, and extends from below upwards in an indefinite manner, even although the primary inflorescence be definite.

Among the _Equisetaceae_ a similar plurality of spikes occurs often as a result of mutilation.[387] The deviation in question might in some instances be turned to good account, as in the _Tritic.u.m_ before mentioned or as in the broccoli shown at fig. 182, though it must be added that the apparent advantages are often counterpoised by some undesirable qualities or by some circ.u.mstance which prevents us availing ourselves of the new condition.

=Multiplication of Bulbs.=--This occurrence has been briefly alluded to previously (see p. 84). The most curious cases are those in which one bulb is placed on the top of another as happened in some bulbs of _Leucoium aestivum_ described by M. Gay.[388] Irmisch described a similar phenomenon in _L. vernum_; and Mr. Moggridge has communicated drawings of a similar formation in the same species grown in the neighbourhood of Mentone.

From the instances cited it is clear that branching of the inflorescence occurs most frequently in those plants naturally characterised by a dense compact mode of growth, whether that be definite or indefinite, as in spikes, umbels, capitula, &c.; so that compound spikes, umbels, &c., are formed in the place of simple ones (see also prolification of the inflorescence, p. 102).